1. Field of the Invention
The present invention relates to an electron-beam exposure apparatus for exposing a printed substrate and the like by the use of an electron-beam. More particularly, the invention relates to an electron-beam exposure apparatus provided with a correction device for correcting deflection distortion which is capable of being constructed economically using a memory device of relatively small capacity.
2. Description of Prior Art
FIG. 1 is a schematic diagram showing a correction device for correcting deflection distortion occurring in conventional electron-beam exposure apparatuses, as disclosed in Japanese Kokai No. 113168/1977. In FIG. 1, reference numeral 10 designates a correction data storing unit for storing data necessary to correct the deflection distortion, and reference numerals 11 and 12 designate data lines for data representing beam positions in the X-axis and Y-axis directions, respectively. The data lines 11 and 12 are connected to either a pattern data storing unit or a pattern data generating unit (not shown). The correction data storing unit 10 is coupled to the X-data line 11 and Y-data line 12 through data lines 13 and 14 for X-address bits and Y-address bits, respectively. The correction data storing unit 10 is also coupled to an X-adder 17 and a Y-adder 18 through an X-correction data output line 15 and a Y-correction data output line 16. In the X-adder 17, the X-correction data is added to the beam position data in the X-axis direction. On the other hand, the Y-correction data is added to the beam position data in the Y-axis direction in the Y-adder 18. The digital outputs of the X-adder 17 and the Y-adder 18 are applied to D/A converters 19 and 20, respectively, to be converted into analog data. A main deflection coil 12 deflects the electron-beam in the X-axis direction according to the output of the D/A converter 19, whereas a main deflection coil 22 deflects the electron-beam in the Y-axis direction according to the output of the D/A converter 20.
The operation of the conventional apparatus will be described with reference to FIG. 1 and FIG. 3(A).
The beam position data which are supplied through the data lines 11 and 12 from either the pattern data storing unit or the pattern data generating unit (not shown), have an accuracy of N-bits in each of the X-axis and Y-axis directions. A deflection area is equally divided by 2.sup.n (n is positive integer satisfying n&lt;N) in both the X and Y directions to thereby obtain lattice pattern points of (2.sup.n +1).times.(2.sup.n +1) as shown in FIG. 3(A). The correction data are measured at these correction data measurement (lattice pattern) points and then correction data of 2.sup.n .times.2.sup.n is obtained by deleting one column and one line in each of the X and Y directions, voluntarily. The correction data 2.sup.n .times.2.sup.n are stored in the correction data storing unit 10. In deflecting the electron-beam, the correction data which have been stored in the correction data storing unit 10 are applied through the data output lines 15 and 16 to the X-adder 17 and the Y-adder 18, respectively, where the X-correction and Y-correction data are added to the X and Y position data to carry out digital correction. The outputs of the X-adder 17 and Y-adder 18 are subjected to D/A conversion in the D/A converters 19 and 20. Thereafter, the thus obtained analog outputs are applied to the main deflection coils 21 and 22 so as to correct the actual position of the electron-beam. In this case, in order to improve the correction accuracy, it has been proposed to increase the number of correction data measurement (lattice pattern) points in the deflection area, i.e., increase the above described "n" to thereby make the division rate finer.
To make it easy to understand the correction operation, a concrete example is where n=3, that is the division rate is 2.sup.3 =8, the division rate being relatively rough, is shown in FIG. 3(A). The left part of FIG. 3(A) illustrates a square electron-beam pattern that is affected by deflection distortion. As shown in FIG. 3(A), the square electron-beam pattern is distorted at the center of each edge like a bobbin. The distortion is measured at the measurement points to be applied to the respective adders 17 and 18 so that the correction is accomplished by subtracting a value corresponding to the distortion from data representing a reference square pattern not distorted. The corrected pattern is as shown in the right part of FIG. 3(A). The corrected pattern is obtained by subjecting the data for each of the measurement points to correction based on the X-correction data and Y-correction data, and therefore the deflection distortion between the adjacent measurement points remains without correction.
With such a conventional apparatus as constructed above, all of correction data are stored in the correction data storing unit 10, and an actual pattern including deflection distortion is subjected to correction in a digital mode. It should be noted that the bobbin-shaped deflection distortion as shown in FIG. 3(A) occurs most frequently, and such a bobbin-shaped figure can be expressed as a cubic function. Accordingly, it is unnecessary to store the correction data for the bobbin-shaped distortion in the correction data storing unit in advance. In other words, while the provision of a cubic-function processing function enables the apparatus to prepare the correction signals with respect to distortions that can be expressed by a cubic function, without the data having to be provisionally stored in the storing unit the memory capacity is nevertheless increased. However, as mentioned above, all of data including the correction data for the bobbin-shaped distortion for instance are stored in the storing unit. To this end, in the case of exposing a printed substance in which deflections having large amplitudes may occur, the correction values becomes larger than those in exposing an ordinary wafer by the use of the conventional apparatus. Accordingly, in order to maintain accuracy in the exposure, it is indispensable to increase the number of measurement points for the correction data, as a result of which the apparatus is made complicated and the manufacturing cost is thus increased.